Intertidal marsh as a source of dissolved inorganic carbon and a sink of nitrate in the Satilla River-estuarine complex in the southeastern US

Total dissolved inorganic carbon (DIC), total alkalinity (TA), pH, and nitrate + nitrite (NOx) data collected during the summer of 1996 in the Satilla River estuary in the southeastern U.S. were used to assess fluxes of DIC and NOx between intertidal marshes and estuarine waters and to model system NOx dynamics. Nitrate and nitrite are produced in the low-salinity portion of the estuary. The intertidal marshes are sites of intensive respiration that export DIC to the estuary and remove NOx. An integrated view is presented on the nitrification and denitrification processes in the marsh/estuarine complex and their relationship to CO2 generation rates. The distribution of NOx in the marsh and estuarine waters indicates that all NOx generated in the marsh-estuary system is removed in the intertidal marshes, most likely via denitrification. Model analysis of NOx and river flow data for three seasons indicates that NOx distribution in the estuarine water is also determined by river flow rates. Export fluxes of NOx to the coastal ocean are insignificant in all seasons when compared to NOx production rates in the entire system; however, they are significantly higher than NOx inputs from the river end member in October 1996. Although only a small fraction (similar to 10%) of DIC generated in the marshes is exported to the coastal sea and around 90% is lost to the atmosphere, it represents a nearly threefold increase in riverine DIC flux to the ocean.